The present invention relates to gas turbine engine casings, particularly for gas turbine engine fan casings and turbine casings, more particularly to an improved acoustic liner or an improved rotor blade track liner for use within the gas turbine engine casing.
Turbofan gas turbine engines for powering aircraft conventionally comprise a core engine, which drives a fan. The fan comprises a number of radially extending fan blades mounted on a fan rotor enclosed by a generally cylindrical fan casing. The core engine comprises one or more turbines, each one of which comprises a number of radially extending turbine blades enclosed by a cylindrical, or frustoconical, casing.
The fan casing is provided with a hook axially upstream of the tips of the fan blades to prevent upstream movement of a detached fan blade.
There is a requirement to provide an acoustic liner within the fan casing axially upstream of the hook.
Conventionally the acoustic liner is secured within the fan casing by fasteners, nuts and bolts or screws, or by adhesive bonding.
However, the fasteners extend radially through reinforced regions of the acoustic liner and these reinforced regions reduce the acoustic liner face area, which reduces the effectiveness to absorb noise, or attenuate sound, and the fasteners produce steps and gaps which affect the aerodynamic flow over the acoustic liner. In one known arrangement the acoustic liner comprises reinforced regions which include a number of honeycomb cells filled with a strong material and an aperture is machined through the reinforced region for a fastener to pass through. Alternatively the acoustic liner comprises a reinforced region, which includes a boss provided in a honeycomb cell and the boss has an aperture for a fastener to pass through as disclosed in our published UK patent application GB2319589A.
The use of adhesive bonding may be used to secure the acoustic liner to the fan casing, but subsequent replacement would be difficult and any damage to the acoustic liner would require repair using filler and this would also interfere with the ability of the fan casing to contain a detached fan blade.
Ideally the acoustic liner would be easy to install and remove or replace.
A fan blade track liner is provided within the fan casing around and adjacent the tips of the fan blades.
Conventionally the fan blade track liner is secured within the fan casing by adhesive bonding.
However, if the fan blade track liner becomes damaged subsequent removal and replacement is difficult and time consuming. Furthermore, during the removal of a damaged fan blade track liner there is a risk of damaging the fan casing and reducing the ability of the fan casing to contain a detached fan blade. It is possible to increase the thickness of the fan casing to allow for possible fan casing damage, however this adds weight to the gas turbine engine.
Ideally the fan blade track liner would be easy to install and remove or replace.
Accordingly the present invention seeks to provide a novel liner for a gas turbine engine casing, which overcomes the above-mentioned problems.